1. Reduced noise
2. Reduced recoil
3. More fun to shoot (in my opinion)
4. a good suppressor has all the benefits of a decent muzzle break and flash suppressor in addition to the effects on sound.

Disadvantages

1. Long wait time
2. longer and slightly heavier gun
3. Cost
4. they can make semiautomatics less reliable in some cases. In my opinion a suppressor is much better served with a bolt action or single shot host.
5. They tend to be more dirty than shooting with out one.